1. Field of the Invention
The present invention relates to establishment and management of a mobile network by mobile routers, where the mobile network is capable of changing its point of attachment to a wide area network (e.g., the Internet) and thus its reachability in its associated topology.
2. Description of the Related Art
Proposals have been made by Internet Engineering Task Force (IETF) groups for improved mobility support of Internet Protocol (IP) based mobile devices (e.g., laptops, IP phones, personal digital assistants, etc.) in an effort to provide continuous Internet Protocol (IP) based connectivity. For example, the IETF has a Mobile IP Working Group that has developed routing support to permit IP nodes (hosts and routers) using either IPv4 or IPv6 to seamlessly “roam” among IP subnetworks. In addition, the Mobile Networks (MONET) group (renamed as the Network Mobility (NEMO) group) has published different Internet Drafts, available on the World Wide Web at the Network Mobility Home Page at the address http://www.nal.motlabs.com/monet/. One exemplary Internet Draft by Thierry Ernst, entitled “Network Mobility Support Terminology”, February 2002, is available on the World Wide Web at the address: http://www.nal.motlabs.com/monet/drafts/draft-ernst-monet-terminology-01.txt, the disclosure of which is incorporated in its entirety herein by reference.
For example, Ernst describes an exemplary mobile network that can be deployed within an airplane, where passengers establish an IP connection of their respective IP host devices (e.g., laptop, digital telephone, personal digital assistant, etc.) to a mobile router within the airplane for on-board Internet access; during the flight, the mobile router within the aircraft may change its point of attachment to the Internet via distinct Internet Service Providers (ISPs), for example by changing connections via respective radio links or geostationary satellite links for transoceanic flights. Note that a passenger also may have his or her own network (i.e., a personal area network) within the mobile network.
According to the NEMO group, a mobile network may be composed by one or more IPsubnets and is connected to the global Internet via one or more Mobile Routers (MR). The mobile router has at least two network interfaces: an egress interface toward the wide area network, and an ingress interface from within the mobile network. Mobile network nodes may include local fixed nodes (LFN) (nodes unable to change their point of attachment while maintaining ongoing sessions), local mobile nodes (LMN) (mobile nodes that belong to the mobile network and able to change their point of attachment within the mobile network or outside the mobile network), and visiting mobile nodes (VMN) (mobile nodes that not belong to the mobile network and that can change their point of attachment from outside the mobile network to inside the mobile network). Each of the nodes may be either a host or a router.
Hence, a mobile router is a router configured for establishing a communication link between the mobile network and an attachment router of a wide area network, such as the Internet, providing connectivity for the mobile network to the wide area network. The mobile router thus serves as a gateway to route packets between the mobile network and the Internet.
A particular concern involves the nesting of multiple mobile networks within each other. FIG. 1 illustrates a mobile network 10 having multiple subnetworks 12a and 12b. In particular, the mobile network 10 includes a mobile router 14a that establishes a link with an attachment router 16a to enable a local node 18 (e.g., 18a, 18b) to communicate with a correspondent node (CN) 20 via the Internet 22. As illustrated in FIG. 1, the mobile router 14a provides a link for the local fixed node 18a and the local mobile node 18b within the subnetwork 12a, and the visiting mobile router 14b provides IP connectivity for the local fixed node 18c within the subnetwork 12b. In addition, since the visiting mobile router 14b relies on the mobile router 14a to establish the link 24 with the attachment router 16a, the mobile router 14a is deemed the top level mobile router (TLMR) that connects the mobile network 10 to the Internet 22.
A problem arises if additional routers attempt to connect to the mobile network 10, in that arbitrary connections may result in inefficient communications. For example, assume mobile routers 14c and 14d are attempting to connect to the mobile network 10: the resulting structure of the mobile routers 14c and 14d connecting to the mobile router 14b may result in an undesirable network configuration that creates substantial delays for nodes 18 connected to the mobile router 14d. 